In analytical treatments, we assume that the molecular axis is along the \(z\)  axis, and the laser field
\(\textbf {E}(t)\)  is located in the \(xz\)  plane with an angle \(\theta \) 
between its major axis and the molecular axis.
Then according to the SFA, the time-dependent dipole moment can be written as [1]}
\(\begin{aligned}\textbf {x}(t)= &i\int _{0}^{\infty }d\tau \big [\xi (\tau )\textbf {d}_{r}^{*}(\textbf {p}_{st}+\textbf {A}(t))e^{-iS(\textbf {p}_{st},t,\tau )}\\ & \times \textbf {E}(t-\tau )\cdot \textbf {d}_{i}(\textbf {p}_{st}+\textbf {A}(t-\tau ))\big ]+c.c. .\\\end{aligned}\) 
